One of the first bits of advice a friend gave me when she found out I was engaged was this: Keep your own bank account. She was older than me -- about 30 -- and coming off an acrimonious divorce. I was 24, sporting a newly shined sparkler on my left hand, and nowhere near imagining the demise of my relationship.

I didn't listen. More than 12 years later, that man is still my husband, we're still going strong, and I never followed her advice. We have only joint accounts. If I am going to live to regret it, I certainly don't yet. The truth is, one person's mistake does not a "money rule" make. But that doesn't mean there are no rules at all.

Every day, couples commit financial sins. Some are bigger than others, but all can ruin marriages and lives if they don't get fixed. Cherie Lowe, a writer from Indiana who runs the blog Queen of Free, knows firsthand how scary money mistakes can be.

"My husband and I made major money mistakes to the tune of $127,482.30. That’s how much debt we wracked up together in the span of nine years," says Lowe, whose forthcoming book Slaying the Debt Dragon: How One Family Conquered Their Money Monster and Found an Inspired Happily Ever After gives tips on getting rid of debt and staying married. "We spent the next four years paying it off."

Impressive, right? But how can others follow suit? We interviewed a variety of financial experts to find out about the most common money mistakes couples make at five different phases in married life. Here they are:

1.) Dating: Failing to plan ahead. One of the mistakes dating couples make is thinking that the way things are while they date is the way things will always be. My husband and I started dating when we were 23 and so stupid. We barely made any money and we spent all of it on vacations and hot air balloon rides and nights at the bar with our friends. It never occurred to us to save. Experts agree this is unwise.

"In an effort to impress each other, we focus all our romantic energies on activities that typically center on money," Lowe says. "From movies and dinner to special gifts and flowers, many a romantic effort can't be sustained after marriage. Make wise choices about the patterns you set to display your love."

2.) Engaged: Planning too extravagant of a wedding. Getting engaged is a whirlwind of love and romance and, of course, cash. Planning a wedding is hella expensive, and that's not even counting all the money dished out for the ring and the parties and the other pieces of living la vida betrothed.

This is the time when people's attitudes about money really start to reveal themselves. If you can't afford a big wedding, don't have one. Same goes for a big ring. Don't marry a man who mortgages his future so you can wear a massive rock. And don't be a woman who wants one.

The most important things cost nothing, says Barbie O’Connor, author of MoneySmarts4U: The Basics. "If you can't plan a wedding that works for both of you, then your life together might not be as wonderful as you think," O'Connor says. "This is when you will earn your diplomatic stars in the family and establish your adult standing with your parents and future in-laws. If you can't say no to them while planning the wedding, then you will not have a chance to later."

3.) Just married: Leaving all the control to one spouse. Many of the conversations that happen in early marriage actually should have happened BEFORE the marriage. But they often don't. So there's one newlywed mistake for you. But also, this is really the time to be saving and planning for the future. And it's vital that BOTH members of the couple pay attention to the finances.

I didn't do this early in my marriage, and it became a problem. I'm better now, but I wish I'd known right from the start that I couldn't task my husband with our entire financial future. I was lucky, too. The problem resolved itself once I decided to put on my big girl pants and get involved.

"Financial bullying frequently happens in relationships where one person is in charge of the purse strings and the other knows nothing about what is going on," says O'Connor.

4.) Married with young children: Having kids you can't afford. We hear conflicting information about having children. Sometimes it's "you'll never feel like you can afford it, so just do it," and sometimes it's "never have a child you can't afford." Always go with the latter. Having children is expensive, especially if you live an an area with a high cost of living.

Gail Cunningham is in the media relations department for the National Foundation for Credit Counseling and sees this financial problem all the time. "Not figuring out and planning in advance for the true cost of having and raising children is a huge mistake," she says. "In some areas, this can include the cost of tuition for private schools from K-12, then orthodontics and cars, followed by college."

5.) Married seniors: Wanting too much. Not planning for retirement is a bad idea early in marriage, but what about once you get there? What are the money mistakes you can still make in your golden years? You'd be surprised, according to O'Connor. The truth is, living on a fixed income can be frightening -- and it can mean having to watch your finances very carefully.

"Health issues, sufficient retirement savings ... or having to help their children with their grandchildren are all issues that have to be faced financially and personally by people as they age," O'Connor says. "To prepare for this time in life, people need to stay physically and mentally active, learn to be happy with less ... and look for pleasure, beauty, and spiritual satisfaction in the world around them."

Once you know the pitfalls, they are easier to avoid. The fact is, mistakes can be made at so many points along the way. But they can also be fixed. Most experts agree on one thing: the key is being on the same page.

"Go over the books each month together, and once a year, go over your entire financial situation, review your goals, and make adjustments," says O'Connor.